The present invention relates to a genetic marker associated with different conformational traits. More specifically, the present invention describes a process wherein a polymorphism in a Pit-1 gene is used to determine traits in animals such as milk production and muscularity with ease.
Selection of a particular trait in a mammal is presently very expensive and very slow. Usually the selection process involves a genealogical evaluation of the mammals history over a long period of time. This evaluation is based on various traits of the mammal or animal such as birth weight, growth weight, build, muscle strength, firmness, marbling, color, and the like.
Most of the selection of a particular trait in an animal to date, involves visually characterizing the specific traits over a time frame or weighing the animal at particular times. The animals with the quality traits that are to be selected are then bred with similar animals such that the particular trait is hopefully dominant in the next generation or the generations to follow.
The present methods for trait selection in mammals are often tedious and open to judgment of an expert in the field, such as a breeder. However, there is never any real assurance that the choice being made will dominate over the forthcoming generations. For example, in order to select a cow that is a good milk producing animal, it takes between 36 to 48 months to make such choice and after the choice is made, it is often based on hypothesis and the breeder""s judgment.
In view of the uncertainty, expense and time involved with the current methods of trait selection in animals, new methods are currently under development which methods utilize a more scientific process which will hopefully improve the selection process.
One such method is the study of candidate genes to determine whether specific genes are associated with conformational traits in mammals and therefore these genes can be used as molecular markers to select particular traits of interest. This method first requires identification of candidate genes or anonymous genetic markers associated with the traits of interest. The candidate gene approach can be successful, but first genes must be identified in the species of interest and correlated to the traits of interest.
The somatotropin system has several genes that may play a role in the control of particular traits in animals since this system is associated with growth, lactation, reproduction and immunity. The somatotropin system is quite complicated and involves at a hypothalamic level, somatocrinin and somatostatin; at a pituitary level, pituitary-specific transcription factor (Pit-1) which is responsible for growth hormone expression in mammals; at a hepatic level, growth hormone receptor and growth hormone plasmatic transport protein; and at a cellular level, growth hormone receptor, insulin-growth factor-1 and insulin growth factor transport protein.
Selection of genes from this somatotropin system that may influence particular traits in animals is quite complicated, since this system has many different functions in different parts of the animal, from the pituitary to the cellular level.
The present invention involves the selection of a gene, the pituitary-specific transcription factor (hereinafter referred to as Pit-1) that can act as a genetic marker to characterize specific traits in animals.
Pit-1 is a member of the POU family of homeo-domain transcription factors and plays an important role in developmental processes. The POU-domain was originally identified as a highly conserved region of 150 to 160 amino acids found in three mammalian transcription factors, Pit-1, Oct-1, Oct-2 and also in the product of nematode gene unc-86 (Herr et al., Genes and Dev. 2: 1513 (1988); Ruvkun and Finnery, Cell 64:475 (1991)).
Pit-1 is a pituitary-specific transcription factor that regulates growth hormone, activates prolactin and has a role in pituitary cell differentiation and proliferation (Steinfelder et al., P.N.A.S., USA 88:3130 (1991). Mutations in the Pit-1 gene responsible for the dwarf phenotypes of the Snell and Jackson mice and lead to anterior pituitary hypoplasia (Li et al., Nature 347:528 (1992)). Moreover, it has been shown that the inhibition of Pit-1 synthesis leads to a decrease in prolactin and growth hormone (GH) expression and to a dramatic decrease in cell proliferation in GH and prolactin producing cell lines (McCormick et al., Nature 345:829 (1990)).
In human, different mutations in the Pit-1 gene have also been reported in patients with familial pituitary hypoplasia (Pfaffie et al., Science 257:1118 (1992)); and in patients with sporadic combined pituitary hormone deficiency (Radovick et al., Science 257:1115 (1992); Tatsumi et al., Nature Genetics 1: 56 (1992).
The cDNA sequence of bovine Pit-1 has been published by Bonder, M. et al, Cell 55 (3): 505-568 (1988)and is shown in FIG. 2 (SEQ ID NO:7).
The Association of Pit-1 polymorphisms with growth and carcass traits in pigs has been described by Yu et al., J. Anim. Sci. 73: 1282 (1995). Yu et al., supra described three Pit-1 polymorphisms in pigs based on two restriction fragment length polymorphisms (hereinafter referred to as RFLP) using a Pit-1 POU-domain cDNA probe and the restriction enzymes BamHI and MspI and a PCR/RFLP using RsaI.
Results from Yu et al.""s, supra, mixed-model analysis revealed that pigs with the MspI CC genotype were associated with heavier birth rate than the DD genotype pigs. Moreover, with the Pit-1 BamHI polymorphisms heavier birth weight was significantly associated with the BB genotype, although the authors cautioned against concluding such association since the BB genotype population was extremely small.
Although Woolard et al., J. Anim. Sci. 72:3267 1994) recognized a HinfI polymorphism at the bovine Pit-1 gene locus, these authors failed to link this mutation to the selection trait in animals. The conclusion drawn in Woolard, supra was that polymorphic fragments that were observed were consistent with autosomal Mendelian inheritance.
There is no disclosure in Yu et al. or Woolard et al of any association of the allele pattern AB with milk production, nor the allele pattern BB with muscularity in animals.
Therefore, the present invention overcomes the disadvantages of the current methods of trait selection in animals by providing a scientific basis for selection of traits by use of a genetic marker.
Moreover, the process described in the present invention can be used to characterize superior milk producing animals from animals having meat producing characteristics.
It has been surprisingly discovered that a polymorphism in the Pit-1 gene can be used to characterize traits such as milk production and muscularity in animals. Two alleles, A and B were distinguished for the Pit-1 gene responsible for the activation of prolactin and growth hormone gene expression. The AA pattern was less frequent than the AB or BB pattern. The significant superiority of the Pit-1 AB pattern or AA pattern over the BB pattern was observed for milk, protein and angularity. Likewise the BB genotype pattern was associated with animal muscularity.
This discovery permits the use of the mutation in the Pit-1 gene to be utilized as a genetic marker to identify certain traits in animals: Once these particular traits are identified, the animals can be sold at market with increased value due to their superior traits.
Accordingly, it is an object of the present invention to provide a genetic marker for trait selection in animals.
In another aspect, the present invention provides a process to characterize animals having superior milk production traits or muscularity traits.
In yet another aspect, the present invention provides genetically engineered animals that have superior milk production, angularity, fat, protein or muscularity traits. These and other objects are achieved by the present invention as evidenced by the summary of the invention, description of the preferred embodiments and the claims.
The present invention thus provides a genetic marker that can be used for trait selection in mammals.
Furthermore, the present invention provides a method to identify a polymorphism present in the Pit-1 gene which polymorphism can be utilized to select superior traits in animals for angularity, fat, muscularity, protein or milk production.
Accordingly, in one of the composition aspects, the present invention relates to a genetic marker used to distinguish amongst animals a trait for milk producing capabilities or meat producing capabilities said genetic marker comprising a mutation in a fragment of a Pit-1 gene, wherein three allele patterns are observed, the fully mutated pattern being indicative.
In the present application, the marker characteristic of milk producing capabilities is called AA for its homozygous state of the allele and the marker characteristic of meat producing capabilities is called BB for its homozygous state.
The sequences of alleles A and B differ only by one transition from the Adenosine in position 1178 of the sequence of FIG. 2 in Pit-1 AA to a guanine, in Pit-1 BB, as demonstrated by the inventors by experiments shown in Example B.
In a preferred embodiment for the present invention, the three allele patterns are distinguished after digestion with a restriction endonuclease, which cleaves the mutated Pit-1 gene fragment and not the non-mutated Pit-1 gene fragment, the fully digested pattern being indicative of a trait for muscularity in said animal, while the intermediate digested/non-digested pattern or the fully non-digested pattern being indicative of a milk producing trait in said animal.
In a more preferred embodiment of the present invention the restriction endonuclease utilized is HinfI.
In another preferred embodiment of the present invention, the three allele patterns are distinguished using probes which overlap the mutated region in said Pit-1 gene, one probe being specific for the mutated Pit-1 gene and another one being specific for the non-mutated Pit-1 gene.
In another aspect, the present invention relates to a process for detecting certain traits in an animal, said process comprising the steps of:
(1) isolating genomic DNA from an animal;
(2) optionally isolating a fragment from said genomic DNA comprising a fragment of a Pit-1 gene;
(3) detecting a mutation in the Pit-1 gene; and
(4) analyzing said mutation to determine a trait in said animal wherein upon analysis traits of muscularity and fat can be distinguished from milk producing traits in said animals.
In particular embodiment of the present invention, detection is accomplished by using restriction endonucleases.
In another particular embodiment of the present invention, detection is accomplished by using probes which overlap the mutated gene in said Pit-1 gene, more particularly the 1178 position.
In yet another aspect, the present invention relates to genetically engineered animals that have the characteristic traits described in the present invention.